This invention relates to the production of carbon black and more particularly to a burner and feedstock injection assembly for a carbon black reactor. The burner is designed for the atomizing and burning of liquid fuels to provide the heat required for the reaction.
Applicant does not claim that the use of liquid fuels in carbon black reactors is necessarily novel per se. For example, the following U.S. patents disclose specific fuel-oil burner injection systems designed for carbon black reactors: U.S. Pat. Nos. Re. 22,886; 2,420,999; 2,641,534; 2,961,300; 3,003,854; 3,060,003; 3,211,532; 3,290,120; 3,501,274; and 3,669,628.
The closest prior art known to the applicant which relates to his burner per se is U.S. Pat. No. 3,254,846 which embodies some of the same principles and configurations at the tip of the burner where the atomization of the fuel oil takes place. It will be noted, however, that said patent does not disclose the improvement of combustion by the use of high swirl numbers characterized by flow reversal zones and backmixing within the flame zone, nor does it disclose the possibility of carbon black manufacturing requiring a flame pattern that allows insertion of a central tube through the heart of the flame for injection of carbon black feedstock. Furthermore, applicant's burner design itself embodies other significant design features which are believed to be patentably different from the burner of said patent.
The principles of applying intensive swirl in burner design are described in the book Combustion Aerodynamics by Beer and Chigier, published (1972) by Halsted Press Division, John Wiley & Sons, Inc., New York, and in reports from the International Flame Research Institute of Ijmuiden.
In many instances natural gas is used as a fuel in carbon black reactors; however, in situations where gas is not available, or is not available at an economic price, it is desirable to have a burner which is designed for the use of liquid fuels, including heavy liquid fuels. The main problem in designing such a burner is that the high velocities required, particularly in carbon black reactors, do not provide enough residence time to provide for complete combustion of the fuel within the time allowed unless the atomization of the fuel is extremely efficient and extremely high rates of combustion are realized.
Conventional methods of high-pressure atomization result in high discharge velocities. The fabrication of the fuel discharge nozzle will determine to what extent the discharge pattern--and therefore the discharge velocity--will be radial or axial. A high axial velocity has the disadvantage of a long, drawnout flame undesirable in carbon black production in which the high velocities of reactants require rapid combustion and a short flame. A high radial velocity causes impingement of droplets on the inside surface of the rather small-diameter combustion chamber, resulting in undesirable coke formation.
For the carbon black process, in accordance with the technology used by the inventor, it is highly advantageous to have a flame of burning fuel enveloping the feedstock injection spray in a zone of high axial velocity, the base of the said flame being upstream of the feedstock injection point. It is also essential that the position of the feedstock oil spray can be moved along the centerline by extending or retracting the tubular feedstock injection subassembly through the burner and through the heart of the flame. This feedstock injection subassembly must be protected against the heat of the flame by internal liquid cooling or by an internal flow of cooling gas.
Broadly speaking, the object of this invention is to provide a burner, for a carbon black reactor, which will provide a high rate of combustion and a satisfactory flame pattern, even when operating with the use of heavy liquid fuel oils. More specifically, the object of the invention is to provide a burner with sufficient flame stability in a zone of high axial flow velocities and a combustion rate so high as to obtain essentially complete combustion a short distance from the burner head using liquid hydrocarbons with high carbon-hydrogen ratios, and using atomizing means that provide extremely fine atomizing while at the same time preventing liquid droplets impinging on the walls of the combustion chamber and causing coke formation such as usually occurs when the atomizing function relies on forcing liquid, air-liquid, or steam-liquid mixtures through small orifices under high discharge pressures. The pattern of discharge should be hollow and, in particular, it should prevent oil still in the liquid phase from coming in contact with the cool pipe of the feedstock injection subassembly.
It is another object of the invention to provide a fuel combustion system for a carbon black reactor that inhibits the formation of air polluting nitrogen oxides. Other objects will be apparent from the description which follows.